The present invention relates generally to voltage regulators and in particular, to methods and circuits for phase shedding.
FIG. 1 shows a conventional 2-phase so-called buck-type DC-DC voltage converter (or regulator). It generally includes a controller 102, phase 1 transistor switches (upper transistor Q1, lower transistor Q2), phase 2 transistor switches (upper transistor Q3, lower transistor Q4), reverse-coupled inductor L1, and output capacitor C1, all coupled together as shown to provide a regulated Dc voltage to a load 104. The reverse coupled inductor L1 comprises first and second windings W1, W2 magnetically coupled to one another, as shown, with like polarities at nodes 1 and 2, on the one hand, and 3 and 4 on the other hand.
Each winding has associated leakage inductance (LL), and the overall inductor has an associated magnetic inductance (LM) such that when current is driven thorough either winding and provided to the load, an induced current is generated in the other winding and also provided to the load. The amount of induced current is: LM/(LL+LM) times the amount of current in the driven winding. As an example, if the windings each have leakage inductance (LL) of 60 μH and the magnetic inductance is 140 μH, then the amount of induced current is 140/200 times the current in the driven winding. Thus, for example, if 10 A is driven through the first winding W1, then 7 A would be induced through winding W2, and the load would receive a total of 17 A. This circuit is sometimes referred to as a “current doubler” (even though the current is normally not quite doubled). (Note that with leakage inductance of 60 μH in each winding, each winding would actually see 120 μH of leakage inductance, which may be favorable since, among other reasons, leakage inductance serves to reduce ripple current and thus switching losses. It should also be appreciated that as used herein, the term: “reverse coupled inductor” refers to any magnetic and/or inductive structure, such as L1, with sufficient leakage inductance for implementing a buck regulator and suitable magnetic inductance for inducing a current in a winding based on a current driven in another winding, whereby the induced and driven currents can feed into a common load. “For example, with a two winding implementation, a two winding transformer with suitable leakage inductance in each winding could be used. On the other hand, a transformer with low leakage could be used in combination with separate inductors electrically coupled in series with each winding. Other structures, whether or not referred to as transformers, inductors, or combinations of the same could also work to implement a reverse coupled inductor.)
The controller controls the windings so that the first winding is driven during a first clock cycle phase (e.g., first half of a clock cycle), with the second winding being driven during the second phase. The controller achieves this by turning on Q1 and Q4 (with Φ1U and Φ2L asserted) during the first phase and turning on Q2 and Q3 (with Φ1L and Φ2U asserted) during the second phase. The controller modulates the duty cycles of the turn-on times in each phase to regulate the generated voltage at the load based on load demands, as indicated with feedback from the load. The result is a regulated DC voltage provided to the load to receive up to twice the current driven through the switch network. This can be an effective voltage regulator design, however, improved efficiencies, especially during low load conditions, may be desired.